It is known to attach condition monitoring units to a train axle or to a bearing thereof in order to monitor parameters such as vibration, temperature and acoustic emission.
Within the automotive sector, there are a plethora of wired sensors, many of which are associated with ECU (Engine Control Unit) and OBD (On Board Diagnostic) systems. These sensors are fully integrated into the vehicle's infrastructure such that during the vehicle's operation they have a continuous power supply. Data communications are supported by a CAN (Controller Area Network) bus. These sensor systems operate continuously to monitor their target parameters.
Locomotives and passenger carriages also have a range of sensor systems that are fully integrated, but these are generally related to safety critical functionality.
Currently available condition monitoring solutions with permanent power sources are configured to capture data continuously. However the captured data generally contain a large volume of artefacts and the measured curves reflect the curviness of the track, imperfections of the rails and other external influences. It is therefore necessary to use complex algorithms to filter the data to eliminate artefacts and to extract valuable and reliable information on the condition of the bearing from the large volume of data.
In order to save power and to ensure good data quality, it has been proposed to limit the measurement to specific sections of a track where low background noise and external factors are expected. To this end, it has been proposed to set predetermined waypoints triggering a measurement based on GPS data. If a certain waypoint along a track is reached, the control unit triggers a signal starting the condition monitoring units to measure the operating parameters of the bearings or other components being monitored and, likewise, the monitoring is stopped if the vehicle leaves the track.
To ensure consistent and reliable data readings, the condition monitoring unit should capture data on a known good quality section of track. Preferably, the track or route should be straight, level and allow the train to reach and maintain a constant speed. Additionally these waypoints are track trigger co-ordinates and function as reference points for data trending as all measurements will therefore be referenced to the same points on the track or route.
Energy consumption can be reduced significantly by powering on and logging data for short periods of time when the correct conditions are met. Triggering measurements on a known piece of track reduces data collection errors or anomalies and optimizes the power usage. The reduced energy consumption may enable using generators or power harvesting means with lower rated power or increase the longevity of batteries.
According to the prior art, these GPS-waypoints triggering the activation or deactivation of the sensor units or condition monitoring units are set manually in advance. This is burdensome and complicated and requires the involvement of skilled engineers having both knowledge of the geographical and technical details of the track and of the technology being monitored.
In applications where no network structure exists or where the condition monitoring unit has to be attached to rotating components, it has been proposed to use wireless nodes. A consideration in the design of wireless sensor systems is the time between maintenance which is frequently dictated by the life of their batteries. As a consequence, power management is an important factor in the design of wireless sensor systems because it has immediate impact on maintenance intervals.
In recent deployments, wireless sensors located on axleboxes communicate back to an on-board system using a local wireless network system which is used to gather sensor data and transfer it remotely. The installation of local wireless network systems on a train may be complicated and the systems are susceptible to failure. Each of these systems has the drawback of having a single point of failure: the on-board system.
The document DE 202005005278 U1 discloses a sensor unit for monitoring the temperature of axlebox bearings of railway vehicles. The document DE 102010027490 A1 discloses a further monitoring system for railway vehicles including a mobile telecommunication device based on the GSM or the UMTS standards.
When using wireless communication devices exchanging data on a permanent basis, there is a significant permanent energy consumption reducing the battery life. In cases where the sensor unit includes power-harvesting circuits, these must be dimensioned so as to yield sufficient energy even for intervals where the train is standing still. The latter intervals are, however, difficult to predict and/or to control for the manufacturer of the sensor unit and any limitation of these intervals would impose additional burdens onto the user of the railway vehicle.